In general, a reciprocal compressor is configured such that a compression space into/from which an operating gas is sucked and discharged is defined between a piston and a cylinder and that the piston is linearly reciprocated in the cylinder to compress refrigerant.
Recently, since the conventional reciprocal compressor includes components such as a crank shaft, etc. to convert a rotation force of a driving motor into a reciprocal linear motion force of the piston, a problem such as a significant mechanical loss occurs due to the motion conversion. A linear compressor has been actively developed to solve this problem.
In this linear compressor, particularly, a piston is connected directly to a linear motor performing reciprocal linear motion, thus eliminating a mechanical loss caused by the motion conversion, improving compression efficiency, and simplifying the construction. In addition, since the operation of the linear compressor can be controlled by adjusting power input to the linear motor, the linear compressor generates less noise than the other compressors, so that it is often applied to electric home appliances such as refrigerators, etc. which are used indoors.
FIG. 1 is a top sectional view illustrating an example of a conventional linear compressor, and FIG. 2 is a side sectional view illustrating part of an example of a linear motor applied to the conventional linear compressor.
As illustrated in FIG. 1, the conventional linear compressor is configured such that a structure body composed of a frame 2, a cylinder 3, a piston 4, a suction valve 5, a discharge valve assembly 6, a motor cover 7, a supporter 8, a back cover 9, a muffler assembly 10, eight springs 20, and a linear motor 30 is elastically supported in a hermetic container 1. Of course, a suction pipe 1a through which refrigerant is sucked and a discharge pipe 1b through which compressed refrigerant is discharged are provided in the hermetic container 1.
The springs 20 are provided to elastically support the piston 4 in the axial direction, wherein four first springs 21 are installed between the motor cover 7 and the supporter 8 and four second springs 22 are installed between the supporter 8 and the back cover 9. Therefore, when the piston 4 moves in the direction of compressing refrigerant, the first springs 21 are compressed to elastically support the piston 4, but when the piston 4 moves in the direction of sucking refrigerant, the second springs 22 are compressed to elastically support the piston 4.
As illustrated in FIGS. 1 and 2, the linear motor 30 is configured such that an air gap is maintained between an inner stator 31 and an outer stator 32 and that a permanent magnet 33 is interposed therebetween to be able to perform reciprocal linear motion. The permanent magnet 33 is connected to the piston 4 by a connection member 34, thereby reciprocally driving the piston 4. The inner stator 31 is formed in a cylindrical shape by stacking laminations in the circumferential direction. Here, one axial end of the inner stator 31 is brought into contact with one surface of the frame 2, and the other axial end of the inner stator 31 is fixed to an outer circumferential surface of the cylinder 3 by a fixing ring (not shown). The outer stator 32 is configured such that a plurality of cores 32B and 32B′ are coupled to a coil winding body 32A at given intervals in the circumferential direction. The core 32B and 32B′ is composed of a pair of blocks 32B and 32B′ and installed to surround the outer circumferential surface of the coil winding body 32A in the axial direction of the coil winding body 32A. The core 32B and 32B′ is provided with a pair of poles 32a and 32b to surround part of the inner circumferential surface of the coil winding body 32A. Of course, the outer stator 32 is installed maintaining the air gap from the outer circumferential surface of the inner stator 31. The outer stator 32 is disposed to be in contact with the frame 2 and the motor cover 7 in the axial direction, and then fixed as the motor cover 7 is bolt-fastened to the frame 2. The permanent magnet 33 has N-S poles. The permanent magnet 33 is provided such that the (N-S) poles are positioned on its face opposite to the inner stator 31 and its face opposite to the outer stator 32, respectively, and connected to the piston 4 by the connection member 34. Accordingly, the permanent magnet 33 performs reciprocal linear motion due to a mutual electromagnetic force between the inner stator 31, the outer stator 32, and the permanent magnet 33, thereby operating the piston 4.
Therefore, since the moving member composed of the piston 4 and the permanent magnet 33 is supported by the mechanical springs 20 on both sides of the linear motion direction relative to the fixed member composed of the cylinder 3 and the stators 31 and 32, if the M-K resonant frequency is calculated that is defined by the mass M of the moving member and the spring constant K of the springs supporting the moving member and the power frequency applied to the linear motor 32 is set to conform to the M-K resonant frequency, efficiency of the linear compressor can be optimized.
The operation of the conventional linear compressor with the above construction will be described in detail.
When power is input to the coil winding body 32A, N/S poles are alternately formed on the inner stator 31 and the outer stator 32, and the permanent magnet 33 interposed therebetween performs reciprocal linear motion due to the attractive or repulsive force according to pole changes of the inner stator 31 and the outer stator 32. Here, if the center of the permanent magnet 33 escapes from the ends of the two poles 32a and 32b of the outer stator 32, the attractive force does not reach the permanent magnet 33 or the external diffusion of the electromagnetic field increases, so that the permanent magnet 33 may be separated from between the inner stator 31 and the outer stator 32 or the externally-diffused electromagnetic field may magnetize the hermetic container 1 or the other components in the hermetic container 1, which leads to low operation reliability. In order to solve the above problem, the stroke of the piston 4, i.e., the moving distance of the permanent magnet 33 is strictly limited such that the center of the permanent magnet 33 moves between the ends of the two poles 32a and 32b of the outer stator 32. For this purpose, as illustrated in FIG. 1, a few mechanical springs 20 made of high-rigidity spring steel are used to elastically support the moving member.
When the linear motor 30 operates as described above, the piston 4 and the muffler assembly 10 connected thereto perform reciprocal linear motion, and, as the pressure of the compression space P varies, the suction valve 5 and the discharge valve assembly 6 perform operation. In this operation, refrigerant is sucked into the compression space P via the suction pipe 1a of the hermetic container 1, an opening portion of the back cover 9, the muffler assembly 10, and an inlet port of the piston 4, compressed in the compression space P, and discharged to the outside through the discharge valve assembly 6, a loop pipe (not shown), and the discharge pipe 1b of the hermetic container 1.
The recent linear compressor has been developed to be easily installed in a small space as well as to be easily applied to a low capacity. However, the conventional linear compressor and the linear motor applied thereto are not suitable for the low-capacity simple construction because the stroke length of the piston 4 is strictly limited to the distance in which the center of the permanent magnet 33 performs reciprocal linear motion between the two poles 32a and 32b of the outer stator 32 due to the aforementioned reasons and a few springs 20 are used for this purpose.